Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$170.40	4.808%	$178.5928	$178.59	$178.60	$178.60
Purchase #2	$66.44	9.730%	$72.9046	$72.90	$72.90	$72.90
Purchase #3	$133.66	9.284%	$146.069	$146.07	$146.05	$146.10
Purchase #4	$89.47	6.198%	$95.0154	$95.02	$95.00	$95.00
Purchase #5	$15.27	3.732%	$15.8399	$15.84	$15.85	$15.80
Purchase #6	$104.62	6.664%	$111.5919	$111.59	$111.60	$111.60
Purchase #7	$135.46	9.334%	$148.1038	$148.10	$148.10	$148.10
7 purchase totals =	$715.32		$768.1174	$768.11	$768.10	$768.10